The disclosure of Japanese Patent Application No. 2005-303248 filed on Oct. 18, 2005, including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a shift control apparatus of a constant mesh transmission. More particularly, the invention relates to a shift control which, when a shift is required, performs an operation to return the shift position from the speed before the shift to neutral in parallel with performing an operation to switch a clutch from an engaged state to a released state.
2. Description of the Related Art
A transmission that includes a constant mesh gear train is known which performs a shift not manually, but automatically using an actuator and the like. In a vehicle provided with such a transmission, a clutch provided between an engine and the transmission is operated by the actuator and the like. In this kind of transmission, a shift is preferably performed quickly during rapid acceleration or starting from a standstill on a hill, for example.
For example, Japanese Utility Model Publication HEI 6-20127 describes a shift control apparatus of a transmission in which a driver can request an early shift when necessary, such as when accelerating rapidly or starting from a standstill on a hill. This shift control apparatus is a shift control apparatus for an electronically controlled mechanical automatic transmission which has a main transmission and sub-transmission with a hi-lo two-speed shifting range. This shift control apparatus is provided with a rapid shift request switch to be used when the driver wants to shift early. The shift control apparatus also has a control device which releases a clutch in response to receiving a signal from the rapid shift request switch and disengages the gear of the main transmission While simultaneously shifting the sub-transmission, and then engaging the gear of the main transmission after that shift operation is complete.
According to the shift control apparatus described in the foregoing publication, the shifting time can be reduced if the shift is performed when a rapid shift switch, which is provided on a shift lever, is on or when an accelerator pedal is being depressed to a kick down region which corresponds to a rapid shift request switch when a rapid shift is required, such as when accelerating rapidly or starting from a standstill on a hill.
In addition, technology is also known which performs a shift either while keeping the clutch engaged or after releasing the clutch depending on the state of the vehicle in order to reduce the shifting time when shifting on an upgrade, for example. For example, Published Japanese National Phase Application 2004-523705 of PCT application describes an automatic mechanical shifting system which issues a command to perform either a dynamic shift operation which is performed while keeping the master clutch engaged, or a dynamic shift operation that is performed to reengage the master clutch after first releasing it. This automatic mechanical shifting system is a vehicular automatic mechanical shifting mechanism which has an operator for an automatic master clutch and a system controller. When performing a dynamic shift operation from a selected speed ratio to a target speed ratio, the system controller uses control logic effective for evaluating which is more effective from among (i) a shift sequence performed while the master clutch is still engaged, and (ii) a shift sequence that includes reengaging the master clutch after it has first been released, and then executing the more effective shift sequence.
According to the automatic mechanical shift system described in the foregoing publication, when performing a dynamic shift operation from a selected speed ratio to a target speed ratio, it is possible to evaluate which is more effective from among (i) a shift sequence performed while the master clutch is still engaged, and (ii) a shift sequence that includes reengaging the master clutch after it has first been released, and then execute the more effective shift sequence.
The shift control apparatus described in Japanese Utility Model Publication HEI 6-20127, however, shortens the shifting time by performing a plurality of continuously performed shift operations in parallel in each of a plurality of transmissions, but does not consider performing a plurality of shift operations in a single transmission Therefore, even if the shifting time is to be shortened by performing an operation to release an engaged clutch in parallel with an operation to return the shift position to neutral during a shift, suddenly interrupting the transmission of power while a large amount of torsion due to torque fluctuation is generated between the input shaft and output shaft of the transmission may result in shock being produced when that torsion is released.
Therefore, while it is possible to control the torque output from the engine like the automatic mechanical shift system described in Published Japanese National Phase Application 2004-523705 of PCT application does, the automatic mechanical shift system described in Published Japanese National Phase Application 2004-523705 of PCT application performs control to reduce the torque output from the engine while the clutch is engaged. Accordingly, no consideration is given to the fact that torque transmitted from the clutch to the transmission fluctuates according to a change in the state of the clutch (such as a change from engaged to released). Therefore, when shift control is to be performed with good responsiveness, shock may be produced by fluctuations in the torque transmitted from the clutch to the transmission.